In many industries it is desirable to print labels, decals or designs, collectively referred to as decorations, on materials such as metal, plastic, glass and ceramic. For example, manufacturers of devices such as cellular telephones and portable computers typically decorate their products with their logo, trademark, etc. to build brand recognition and goodwill towards their company. In addition, components such as keyboard keys need to be decorated with letters, numbers and other symbols.
In such applications, the decorations are typically required to meet minimum adhesion and abrasion standards, as specified by the manufacturer. The adhesion standard measures the attraction between the decoration and the component and is typically measured by what is known in the industry as a "tape test." Under this test, a piece of adhesive tape is applied to the decoration and then pealed away from the decoration. The tape is then visually inspected to determine if a portion of the decoration was removed by the adhesive tape. This is a go/no go test in that the decoration tails it any of the decoration is lifted by the tape, whereas it passes if the tape is clean. The level of adhesion required by the manufacturer is thus a function of the tape specified for the tape test.
The abrasion test is used to measure the decoration's resistance to wear. Wear resistance is especially critical in applications such as cellular phones, where the decoration is exposed to a high level of rubbing, e.g. from the user's fingers. The abrasion test is performed using a specific abrasion tester, such as an abrasion wear tester as manufactured by Norman Tool, Inc. of Evansville, Ind. The abrasion wear tester rubs an abrasive material over the decoration at a constant load for a specified number of cycles. Since the load and the abrasiveness of the abrasion material are constant, the amount of material removed by the tester per cycle is function of the hardness of the material being tested. After the decoration has been abraded for the specified number of cycles, it is visually inspected with a magnifying glass to determine if an excessive amount of wear has occurred. Again, this is a go/no go test in that the decoration fails if it is worn to the point where the underlying component is visible through the decoration, whereas the decoration passes if the component is not visible through the decoration.
Traditionally, decorations have been prepared by applying printing ink directly to the component and, in some instances, a layer of top coat material is also applied over the ink. However, as new materials are used to produce components, these traditional decorating methods sometimes tail to meet the abrasion and adhesion standards specified by the manufacturer. Hence, it is desirable to provide decorating method which will meet these standards on a wide variety of materials.